Flotation apparatus

ABSTRACT

Flotation apparatus comprising an elongated tank having at one end both a submerged feed inlet and an upper froth overflow, a clarified effluent overflow at the opposite end, and a bottom outlet for removing settled solids. A mixing valve assembly is associated as a feed inlet for admixing an aeration stream with the primary feed as it enters the tank; and a trap is provided adjacent the feed inlet for removing relatively large air bubbles from the feed before it enters the main flotation zone.

United States Patent Haymore [451 Ju1y25,1972

[54] FLOTATION APPARATUS Ralph B. Haymore, Salt Lake City, UtahEnvirotech Corporation, Salt Lake City, Utah 22 Filed: Aug. 13, 1970[21] Appl.No.: 63,445

[72] Inventor:

[73] Assignee:

[52] U.S. Cl ..2l0/22l, 137/604, 137/606, 209/170, 210/220, 210/225 [51]Int. Cl ..B01d [58] Field ofSearch ..209/168, 170; 261/87, 93; 210/221,225, 226, 44, 220; 137/604, 606

[56] References Cited UNITED STATES PATENTS 1,014,328 1/1912 Podlesak..137/606 X 1,036,758 8/1912 Walters et al.... ....137/606 X 2,813,07411/1957 Banks et a1 ....2l0/22l X 3,121,680 2/1964 ....210/221 X3,418,236 12/1968 ....2l0/221 X 3,446,488 5/1969 ....210/221 X 3,301,7791/1967 Kovacs. ....2l0/221 X Primary Examiner-Robert L, Lindsay, .lr.Attorney-Richard F. Bojanowski, William S. Britt, C. Harvey Gold andDavid V. Trask ABSTRACT Flotation apparatus comprising an elongated tankhaving at one end both a submerged feed inlet and an upper frothoverflow, a clarified effluent overflow at the opposite end, and abottom outlet for removing settled solids. A mixing valve assembly isassociated as a feed inlet for admixing an aeration stream with theprimary feed as it enters the tank; and a trap is provided adjacent thefeed inlet for removing relatively large air bubbles from the feedbefore it enters the main flotation Zone.

7 Claims, 3 Drawing Figures PATENTEnJuL 25 m2 INVENTOR. RALPH B. HAYMOREATTORNEY F LOTATION APPARATUS BACKGROUND OF THE INVENTION Flotationcells are well known. One form comprises a tank into which feed isintroduced while froth and clarified liquid are discharged therefrom.Flotation of suspended solids is effected by air, or other gasintroduced as an aerated liquid stream into a lower part of the tank.Gas is released as minute bubbles which combine with solids to form abuoyant froth which rises to the surface for collection and treatmentfor solids recovery. In such operations, introduction of the flotationgas may be accomplished by mixing with the primary feed a relativelysmall aeration stream (i.e. a pressurized liquid containing dissolvedgas). Such techniques are feasible, but the mechanism for mixing thefeed and aeration stream is often unwieldy and inefficient. Also, whenthe aeration stream is mixed with the feed under reduced pressures somelarge gas bubbles form which rise rapidly to the surface where theyburst and destroy froth.

OBJECTS OF THE INVENTION It is an object of this invention to provideways and means in a flotation system whereby the primary solids-bearingfeed is more efficiently admixed with pressurized aerated liquid toachieve maximum froth formation.

Another object is the provision, in flotation apparatus, of a trap forintercepting and removing relatively large gas bubbles, before theirentry into the flotation zone thereby to prevent froth destruction dueto bursting of said bubbles adjacent the liquid surface.

Still another object is to provide as an article of manufacture an inletvalve assembly adapted to receive and mix the primary feed stream andthe aeration stream.

DESCRIPTION OF THE INVENTION In brief, the invention provides ways andmeans for flotation in which improved mixing of the primary feed andaeration streams is accomplished and flotation efficiency is furtherenhanced by separation of undesirably large gas bubbles prior toflotation.

The flotation apparatus comprises an elongated, usually rectangularflotation tank, a surface skimming means for froth removal, a bottomsludge discharge, a valve assembly adjacent one bottom end of the tankfor mixing together and introducing into the tank a primary feed and anaeration stream, the valve assembly being so arranged that the aerationstream undergoes a pressure reduction substantially at the point whereit combines with the primary feed stream; and a trap interposed betweensaid valve assembly and the final flotation zone of the tank forremoving from the resulting mixture relatively large gas bubbles priorto final flotation.

A better understanding of the invention may be attained by a perusal ofthe following description in conjunction with the accompanying drawingswhich are offered by way of illustration only and are not to be taken aslimiting the invention, the scope of which is defined by the appendedclaims and equivalents thereof.

FIG. 1 is a perspective view of a rectangular tank embodying theinvention, certain parts being omitted and some internal features beingshown in dotted lines for purposes of clarity.

FIG. 2 is a partial sectional view of a flotation tank.embodying theinvention.

FIG. 3 is an enlarged side sectional view of a mixing valve of the typeemployed in the apparatus illustrated in FIG. 2.

As illustrated, the flotation apparatus comprises a rectangular tankhaving at one end both a froth discharge sump l1 and a feed conditioningchamber 12.

Froth collected on the liquid surface is pushed over the upturned edgeof a shelf 13 into a sump 11 by flights of an upper endless chain rakemechanism 14. The rake mechanism may be driven by any suitable means.Froth discharges from the sump via an outlet 15.

Adjacent the opposite end of the tank is a transversely extending frothrestraining bafile 16 under which clarified liquid flows to exit over atransverse weir 17 to a suitable launder 17a, for final discharge. Thefroth baffle 16 extends clear across the tank; its lower edge is locatedwell below the liquid level but above the tank bottom and it extendsupwardly to an elevation sufficiently above the weir 17 that froth isblocked from entering the launder. It should also be noted that the up-.turned edge of the froth discharge shelf 13 is at an elevation belowthe top of the baffle 16, but just above the overflow weir 17.

The feed conditioning chamber 12 (FIG. 2) includes a mixer-inlet valveassembly 18, hereinafter described in more detail, which receives andmixes the primary feed and an aeration stream. (As used herein, the termaeration stream means a liquid that contains air or other gas which isreleasable as bubbles when pressure on the stream is reduced.) Theresulting mixture is injected into a conditioning zone, subjectedtherein to the separation of undesirably large bubbles by meanshereinafter described. The thus conditioned feed then flows into thetank proper where the released air, combined with solids as a buoyantfroth, rises to the liquid surface for discharge. Because of the slopingtop wall, the conditioning zone increases in cross sectional area andvolume in the direction of flow. This results in a reduced velocity ofthe incoming feed thus maximizing the time for large bubble separation.

A sludge pocket 19 is defined on the tank bottom between a transverselyextending concave baffle 21 and the end of the tank. Settled sludge israked over this baffle into the pocket by the flights of a suitablypositioned endless chain rake mechanism 22 which is similar inconstruction to the upper rake assembly 14 and may conveniently bedriven by a chain 23 in turn driven by such upper rake mechanism 14. Asuitable valve 24 is provided to regulate the rate of sludge withdrawalfrom the pocket.

The valve assembly 18 is mounted at one end of the tank just below thefroth sump 11. It comprises a main chamber 26, a main inlet 27 forreceiving the primary feed stream and an outlet port 28 providingcommunication with the feed conditioning chamber 12 of the tank.

A secondary valve mechanism 31 is also provided, this comprises valvehousing 32, an inlet 33 to the housing, an elongated discharge tube 34extending therefrom and a flow regulator which includes a handle 36, astem 37 extending from the handle axially through the housing anddischarge tube, and a disc 38 secured to the free end of the stem inposition to throttle flow by covering and uncovering the discharge tubeupon reciprocation of the stem by appropriate movement of the handle. Abiasing spring 39 which may have adjustable tension means encircles thestem between the handle 36 and housing 32 and urges the disc toward thenormally closed position. The size of the annulus opening between disk38 and nozzle 34 is thereby regulated. In this manner a predeterminedback pressure can be maintained on the incoming aeration stream in thehousing.

The secondary valve is positioned so that the outlet end of thedischarge tube 34 is aligned with and positioned concentrically withinthe outlet port 28 leading from the chamber 26 into the tank.Preferably, the end of the tube is in about the same plane as the wallof the chamber 26. Both the tube 34 and the cover disk 38 are of smallerdiameter than the outlet port 28 so that primary feed flow may continueeven when the discharge tube 34 is entirely closed.

In accordance with the invention, the entire secondary valve unit 31 ismade to be detachably secured to the valve assembly by suitablefasteners such as bolts 40. Also, the entire valve assembly 18,including the secondary valve 31, is made as a detachable unit.

The sloping bottom 41 of the froth sump ll forms an inwardly andupwardly sloping top wall of the feed conditioning chamber 12. Adownward extension 42a of the inner wall 42 of the sump forms a gasinterceptor or trap in the form of an inverted channel 43 extendingtransversely of the tank. As shown in FIG. 1, one end of the channel 43communicates with an open-top wet well 44 mounted on the side of thetank and extending upwardly above the liquid level. This serves as avent for gas bubbles escaping from the trap. If desired, the tank may beso constructed that the channel slopes upwardly toward the wet well toenhance gas escape.

In operation, the primary feed stream along with any desired frothingagent is introduced into the valve chamber 26 via inlet 27 and flowsinto the conditioning zone of the tank through the outlet 28. Thepressurized aeration stream, containing dissolved air, is introducedinto the secondary valve through inlet 33 thence flows, at a rateregulated by disk 38, out through the discharge tube 34 where it mixeswith the primary feed stream to form a solids bearing froth which willeventually rise to the surface for collection.

Construction of the valve assembly is such that primary feed mixes withthe aeration stream simultaneously with the reduction in pressure on theaeration stream as it exits the discharge tube 34. This insures goodmixing of the primary feed and aeration streams as it enters theconditioning zone. In the latter zone, the mixture has some time tostabilize before entering the tank proper.

The aeration stream contains dissolved and/or entrained air which isreleased as minute bubbles when pressure is reduced as the stream exitsthe discharge tube 34. Air that is not properly dissolved may show up asundesirably large bubbles that rise rapidly to the surface where theyburst with a resultant destruction of froth and the sinking of solids.In accordance with the invention, this is prevented by the bubbleinterceptor or trap 43. Specifically, large bubbles rise rapidly to thetop wall 41 thence flow upwardly therealong to the trap 43 whence theyare blocked from further movement and directed to the wet well 44 wherethey surface and burst harm lessly outside of the main tank area. Thefiner bubbles flow under the trap into the tank proper.

Action at the liquid surface in the wet well will be relatively violent.As a result, froth accumulating there will disintegrate and the includedsolids will resettle through the lower part of the wet well back intothe tank for reflotation and discharge as froth.

I claim:

1. Flotation apparatus comprising an elongated tank with effluentdischarge means for maintaining a fixed upper elevation of liquidtherein, removal means for removing froth from the surface of saidliquid, means for removing sludge from the bottom of said tank, valvemeans for introducing a pressurized aerated primary feed stream intosaid tank, a wall sloping upwardly from said valve means and terminatingat a point intermediate said valve means and said removal means and agas intercepting means located near the top of said sloping wall forintercepting and removing relatively large air bubbles released fromsaid stream before said bubbles reach the surface of said liquid.

2. The apparatus of claim 1 wherein the valve means for introducing anaerated primary feed stream includes:

a. pressure reduction means for introducing an aerated liquid influentstream into said tank through a feed inlet located at one end thereofand near the tank bottom; and

b. means for introducing a solids contaminated liquid streamsubstantially concentrically about the aerated liquid influent stream.

3. The apparatus of claim 1 wherein the means for introducing an aeratedprimary feed stream includes a valve apparatus communicating with feedinlet located at one end of said tank and near the bottom thereof, saidvalve comprising a housing having inlet and discharge ports forreceiving and discharging an aerated liquid influent stream, saiddischarge port associated with a disk to regulate flow by regulating thesize of the annulus opening between said disk and said port, said diskconnected to a stem passing through said housing to an external handle,and main chamber for receiving a solids contaminated liquid stream andhavingfan outlet port ali ned and positioned concentrically with theischarge port for ischarging the aerated liquid influent stream.

4. The apparatus of claim 3 wherein the valve stem has an externalspring associated therewith to urge said disk to a normally closedposition.

5. The flotation apparatus of claim 1 wherein said gas interceptingmeans comprises an overhead cavity for collecting large bubbles, saidcavity having means for discharging same externally to the liquidcontained in said tank.

6. The flotation apparatus of claim 1 wherein said gas interceptingmeans comprises a baffle extending downwardly from the top of said tankto a point beyond said sloping wall to define an inverted channeltherewith, and conduit means providing communication between saidchannel and the outside of said tank at an elevation at least as high assaid fixed upper elevation liquid.

7. Flotation apparatus comprising an elongated tank with effluentdischarge means for maintaining a fixed upper elevation of liquidtherein and means for removing froth from the surface of said liquid,means for removing sludge from the bottom of said tank and valve meansfor introducing an aerated primary feed stream into said tank through anoutlet near the bottom of said tank at one end thereof, said valvecomprising a housing having inlet and discharge ports for receiving anddischarging an aerated liquid influent stream, said discharge portassociated with a disk to regulate flow by regulating the size of theannulus opening between said disk and said port, said disk connected toa stem passing through said housing to an external handle, and mainchamber for receiving a solids contaminated liquid stream and having anoutlet port aligned and positioned concentrically with the dischargeport for discharging the aerated liquid influent stream.

1. Flotation apparatus comprising an elongated tank with effluentdischarge means for maintaining a fixed upper elevation of liquidtherein, removal means for removing froth from the surface of saidliquid, means for removing sludge from the bottom of said tank, valvemeans for introducing a pressurized aerated primary feed stream intosaid tank, a wall sloping upwardly from said valve means and terminatingat a point intermediate said valve means and said removal means and agas intercepting means located near the top of said sloping wall forintercepting and removing relatively large air bubbles released fromsaid stream before said bubbles reach the surface of said liquid.
 2. Theapparatus of claim 1 wherein the valve means for introducing an aeratedprimary feed stream includes: a. pressure reduction means forintroducing an aerated liquid influent stream into said tank through afeed inlet located at one end thereof and near the tank bottom; and b.means for introducing a solids contaminated liquid stream substantiallyconcentrically about the aerated liquid influent stream.
 3. Theapparatus of claim 1 wherein the means for introducing an aeratedprimary feed stream includes a valve apparatus communicating with feedinlet located at one end of said tank and near the bottom thereof, saidvalve comprising a housing having inlet and discharge ports forreceiving and discharging an aerated liquid influent stream, saiddischarge port associated with a disk to regulate flow by regulating thesize of the annulus opening between said disk and said port, said diskconnected to a stem passing through said housing to an external handle,and main chamber for receiving a solids contaminated liquid stream andhaving an outlet port aligned and positioned concentrically with thedischarge port for discharging the aerated liquid influent stream. 4.The apparatus of claim 3 wherein the valve stem has an external springassociated therewith to urge said disk to a normally closed position. 5.The flotation apparatus of claim 1 wherein said gas intercepting meanscomprises an overhead cavity for collecting large bubbles, said cavityhaving means for discharging same externally to the liquid contained insaid tank.
 6. The flotation apparatus of claim 1 wherein said gasintercepting means comprises a baffle extending downwardly from the topof said tank to a point beyond said sloping wall to define an invertedchannel therewith, and conduit means providing communication betweensaid channel and the outside of said tank at an elevation at least ashigh as said fixed upper elevation liquid.
 7. Flotation apparatuscomprising an elongated tank with effluent discharge means formaintaining a fixed upper elevation of liquid therein and means forremoving froth from the surface of said liquid, means for removingsludge from the bottom of said tank and valve means for introducing anaerated primary feed stream into said tank through an outlet near thebottom of said tank at one end thereof, said valve comprising a housinghaving inlet and discharge ports for receiving and discharging anaerated liquid influent stream, said discharge port associated with adisk to regulate flow by regulating the size of the annulus openingbetween said disk and said port, said disk connected to a stem passingthrough said housing to an external handle, and main chamber forreceiving a solids contaminated liquid stream and having an outlet portaligned and positioned concentrically with the discharge port fordischarging the aerated liquid influent stream.